Ok, first of all, I have been gone a while, so please forgive me if this has been covered before.

I am diabetic. I "shoot up pig dope", (insulin), every day.

I discovered recently, that the plastic 'protectors' on the hypo needles, fit perfectly inside a 1/2" pvc pipe.

The picture shows the needle container before use. The needle container after use, (and the needle has been thrown away) And the needle container made into a dart.

To make a dart of this, you simply make a small hole in the tip of it, then screw a drywall screw into it.

Longer darts fly straighter and more accurately. About a 3 inch screw is pretty close to optimum for accuracy. And for penetration of the target. Get too short, and they tend to just flop end over end. The shown dart is close to too short, and is not very accurate.

It is kind of the luck of the, (manufacturing), draw, whether it will be a loose fit, or a tight one in the 1/2" pvc pipe.

If your darts are too loose, and keep sliding down the barrel, simply use a small pair of vise-grips and 'crimp' a tiny portion of the outer lip.

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Now for the question.

I want to build something small. As close to pistol size as possible. But still use the 1/2" PVC barrel and my one inch piston valve. (Actually, I'd love to use a QVC three way, or something of that sort, but those are out of my price range for now.)

In other words, "full size", but as small as possible.

What is the optimum shortest barrel length, for say an accurate 10 to 25 foot shot, and penetration through 1/2" plywood ?

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Last edited by Selador on Fri Apr 06, 2012 5:24 pm, edited 1 time in total.

DEATHSTAR wrote:IF you use a yellow color, "Ideal" brand wire-nut,As the "base" rather than those flimsy plastic insulin things, It will be a bit more "substanstial" IMO.

The diameter is about exactly the same as an AA battery.

IF you want more velocity you are going to need higher pressure.Bottom line ,IMO.

Price of QEV is low. So I recommend "GETTING" the $$$ somehow.Even then to go to higher pressure, you'll need to build a piston valve.OR use a burst-disc. IMO.

Double the pressure and you'll double velocity (as a great spudder once stated)...

Otherwise go for larger diameter and use a sabot type method.

These are not flimsy by any means. They are just as "stout" as the wire nut.

And they fill the barrel completely.

The yellow wire nuts, and AA batteries leave a gap around them in a 1/2" pvc pipe.

Best of all, they are "free" to me. LOL

I'm not a newby, I do know about pressure, velocity, etc. Just can't remember how I originally figured out optimum barrel length.

I said I can't afford the QEV. ("low" price, is relevant. If you don't have a dollar, 2 dollars is expensive.)

Someday, I will.

Until then, as I have also already said, I already have a 1" piston valve. One I built myself. And from tests back then, built as well and performs as well as any on here. (Better than some. ) (I put a glass marble through 3/4" plywood that was soaked through and through. Harder to penetrate wet plywood. The fibers tend to stretch and deform, rather than just break. Then, after going through the plywood, it went through a fiberglass window cover. The window. And then two cupboards, inside, which start about 7 feet from the window. All this when shot from more than 40 feet away from the plywood. Believe me. I do know the basic principles of spudgun mechanics. LOL Just have forgotten the way I figured barrel length.)

I also have modified a sprinkler valve. And have that available. (It also works beautifully.)

I am considering the coax, though, because once you incorporate the sprinkler valve, piston valve, etc, it starts to get bigger than I want it to be.

What I like about the coax, is that with the other setup, the barrel starts way out there in front of you. Then there is all the barrel length after that.

But with a coax, the barrel begins pretty close to the back end of the gun. Somewhere close to where you will be holding the gun. So the full length of the overall gun is much shorter.

Maybe just a coax with the sprinkler valve on the back end of it.

4 Inch pipe is doable as the outer pipe. As is 2 and 3 inch.

I just need to know that optimum shortest barrel length, to get started.

You can run GGDT by installing WINE and VB6 runtime dll's using winetricks. It's extremely simple in Mint. I don't think I've ever had a linux distro installed without GGDT, HGDT, and Roller Coaster Tycoon running through WINE.

mark.f wrote:You can run GGDT by installing WINE and VB6 runtime dll's using winetricks. It's extremely simple in Mint. I don't think I've ever had a linux distro installed without GGDT, HGDT, and Roller Coaster Tycoon running through WINE.

I refuse to install wine and the windows dlls, etc, for the same reason I stopped using windows in the first place.

That's kind of like buying a small car for the gas mileage, then dropping an 8 cylinder small block in it. What was the point ? You bought it for gas mileage, then you threw the gas mileage out the window.

If it doesn't run in linux, it doesn't get run on my machine.

You know, come to think of it, I think I used GGDT, way back when I first figured out what size barrels I wanted to use. LOL

Crna Legija wrote:as for barrel length that changes with chamber size so you have to find one out before getting the other.

just go with a 1-1 barrel chamber ratio and you'll be golden

THAT was it !

Thank you very much.

As I remember it, a 2 inch pipe has more than double the volume of a one inch pipe. And so on.

Ok, so starting with one foot of 2 inch pipe.

First of all, the 'volume' that will be taken up with the 1/2" pipe is equal to the overall area of the pipe itself. Not the inner volume of the pipe. So I have to figure that out, and subtract that from the volume inside a 2 inch pipe.

Plus, whatever volume is displaced by the 'valve' end of things. LOL

Or I could just wing it. A foot of 2" for the chamber. About a foot and a half of 1/2 inch, for the barrel. And figure out the valve end based on 1 inch pipe and a piston that will fit inside it.

Let's say you're happy with a 1 1/2' 1/2" barrel, then GGDT tells me that you won't see much improvement with a 1" diameter 1' long chamber. Increasing the chamber size will marginally increase velocity.

Now if you wanted a coax with the same length barrel, then a 2" chamber the same length as the barrel will give you much the same performance.

If you want some numbers run in GGDT, post them here, or there's a GGDT/HGDT request thread in General (I think).

Zeus wrote:Let's say you're happy with a 1 1/2' 1/2" barrel, then GGDT tells me that you won't see much improvement with a 1" diameter 1' long chamber. Increasing the chamber size will marginally increase velocity.

Now if you wanted a coax with the same length barrel, then a 2" chamber the same length as the barrel will give you much the same performance.

If you want some numbers run in GGDT, post them here, or there's a GGDT/HGDT request thread in General (I think).

I believe I said... 1 foot of 2" chamber. Not 1".

As I said above, I was thinking 1 foot of 2" for chamber. And 1 and a 1/2 foot of 1/2" for the barrel.

So you are suggesting a 2" chamber the same length as the barrel ? Or in other words, 1 and 1/2 feet of 2" ???

As I said above, I was thinking 1 foot of 2" for chamber. And 1 and a 1/2 foot of 1/2" for the barrel.

So you are suggesting a 2" chamber the same length as the barrel ? Or in other words, 1 and 1/2 feet of 2" ???

I'll go look for that request thread. Thank you.

yeah you did say that but zeus said their aint much difference performance wise between 1' of 2'' and 1' of 1''. If you realy want the 2 inch chamber go with a much longer barrel to use the extra air something like 3-4 foot long.

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--Homer Simpson

Crna Legija wrote:yeah you did say that but zeus said their aint much difference performance wise between 1' of 2'' and 1' of 1''. If you realy want the 2 inch chamber go with a much longer barrel to use the extra air something like 3-4 foot long.

Ah.

I can see the point.

I didn't read his post that way.

It looked to me like he just made a typo on that first sentence.

It's been more than a few seconds, since I made the request at the GGDT request thread, so I think I am going to ask for my money back.

At this point, it is looking like a 1-1/2 foot 2" chamber. With a 1-1/2 to 2 foot 1/2" barrel, in a coax build.

Tough parts for me will be to get the barrel in there, keeping it square, without having to use screw together fittings at the bulkhead. And the same for the piston and it's pipe... Keeping it square to the barrel.

hmm, sized and stuff, with my build i just winged it myself, and adjusted pressure until i got a good result...

nevertheless i made a drawing of o coax idea i wanted to try myself a soon as i know how to make it

ill post it here, so you can ponder if it will work... i was trying to do the same when i made this drawing, i still have to start actually building tough...
basicly i wanted the small pacage from a coax, and the possibility to add a magazine...thus i needed a breech...

i dont know how to make the "donut" besides casting it from epoxy... around some pieces of pipe... but there are more ways to do it